Toshihide Shibazaki

KGA-2727, a Novel Selective Inhibitor of a High-Affinity Sodium Glucose Cotransporter (SGLT1), Exhibits Antidiabetic Efficacy in Rodent Models

The high-affinity sodium glucose cotransporter (SGLT1) plays a critical role in glucose absorption from the gastrointestinal tract. We have developed 3-(3-{4-[3-(β-d-glucopyranosyloxy)-5-isopropyl-1H-pyrazol-4-ylmethyl]-3-methylphenoxy}propylamino)propionamide (KGA-2727), which has a pyrazole-O-glucoside structure, as the first selective SGLT1 inhibitor. KGA-2727 inhibited SGLT1 potently and highly selectively in an in vitro assay using cells transiently expressing recombinant SGLTs. In a small intestine closed loop absorption test with normal rats, KGA-2727 inhibited the absorption of glucose but not that of fructose. After oral intake of starch along with KGA-2727 in normal rats, the residual content of glucose in the gastrointestinal tract increased. In the oral glucose tolerance test with streptozotocin-induced diabetic rats, KGA-2727 attenuated the elevation of plasma glucose after glucose loading, indicating that KGA-2727 improved postprandial hyperglycemia. In Zucker diabetic fatty (ZDF) rats, chronic treatments with KGA-2727 reduced the levels of plasma glucose and glycated hemoglobin. Furthermore, KGA-2727 preserved glucose-stimulated insulin secretion and reduced urinary glucose excretion with improved morphological changes of pancreatic islets and renal distal tubules in ZDF rats. In addition, the chronic treatment with KGA-2727 increased the level of glucagon-like peptide-1 in the portal vein. Taken together, our data indicate that the selective SGLT1 inhibitor KGA-2727 had antidiabetic efficacy and allow us to propose KGA-2727 as a candidate for a novel and useful antidiabetic agent.

Chronic receptor-mediated activation of Gi/o proteins alters basal t-tubular and sarcolemmal L-type Ca2+ channel activity through phosphatases in heart failure

L-type Ca(2+) channels (LTCCs) play an essential role in the excitation-contraction coupling of ventricular myocytes. We previously found that t-tubular (TT) LTCC current density was halved by the activation of protein phosphatase (PP)1 and/or PP2A, whereas surface sarcolemmal (SS) LTCC current density was increased by the inhibition of PP1 and/or PP2A activity in failing ventricular myocytes of mice chronically treated with isoproterenol (ISO mice). In the present study, we examined the possible involvement of inhibitory heterotrimeric G proteins (G(i/o)) in these abnormalities by chronically administrating pertussis toxin (PTX) to ISO mice (ISO + PTX mice). Compared with ISO mice, ISO + PTX mice exhibited significantly higher fractional shortening of the left ventricle. The expression level of Gα(i2) proteins was not altered by the treatment of mice with ISO and/or PTX. ISO + PTX myocytes had normal TT and SS LTCC current densities because they had higher and lower availability and/or open probability of TT and SS LTCCs than ISO myocytes, respectively. A selective PKA inhibitor, H-89, did not affect LTCC current densities in ISO + PTX myocytes. A selective PP2A inhibitor, fostriecin, did not affect SS or TT current density in control or ISO + PTX myocytes but significantly increased TT but not SS LTCC current density in ISO myocytes. These results indicate that chronic receptor-mediated activation of G(i/o) in vivo decreases basal TT LTCC activity by activating PP2A and increases basal SS LTCC activity by inhibiting PP1 without modulating PKA in heart failure.

Structure-activity relationship studies of 4-benzyl-1H-pyrazol-3-yl β-d-glucopyranoside derivatives as potent and selective sodium glucose co-transporter 1 (SGLT1) inhibitors with therapeutic activity on postprandial hyperglycemia.

Sodium glucose co-transporter 1 (SGLT1) plays a dominant role in the absorption of glucose in the gut and is considered a promising target in the development of treatments for postprandial hyperglycemia. A series of 4-benzyl-1H-pyrazol-3-yl β-d-glucopyranoside derivatives have been synthesized, and its inhibitory activity toward SGLTs has been evaluated. By altering the substitution groups at the 5-position of the pyrazole ring, and every position of the phenyl ring, we studied the structure-activity relationship (SAR) profiles and identified a series of potent and selective SGLT1 inhibitors. Representative derivatives showed a dose-dependent suppressing effect on the escalation of blood glucose levels in oral mixed carbohydrate tolerance tests (OCTT) in streptozotocin-nicotinamide-induced diabetic rats (NA-STZ rats).

Design, synthesis, and structure–activity relationships of a series of 4-benzyl-5-isopropyl-1H-pyrazol-3-yl β-d-glycopyranosides substituted with novel hydrophilic groups as highly potent inhibitors of sodium glucose co-transporter 1 (SGLT1)

Sodium glucose co-transporter 1 (SGLT1) plays a dominant role in the absorption of glucose in the gut and is considered a promising target in the development of therapeutic options for postprandial hyperglycemia. Previously, we reported potent and selective SGLT1 inhibitors 1 and 2 showing efficacy in oral carbohydrate tolerance tests in diabetic rat models. In a pharmacokinetic (PK) study of 2, excessive systemic exposure to metabolites of 2 was observed, presumably due to the high permeability of its aglycone (2a). To further improve SGLT1 inhibitory activity and reduce aglycone permeability, a series of 4-benzyl-5-isopropyl-1H-pyrazol-3-yl β-D-glycopyranoside derivatives bearing novel hydrophilic substitution groups on the phenyl ring were synthesized and their inhibitory activity toward SGLTs was evaluated. Optimized compound 14c showed an improved profile satisfying both higher activity and lower permeability of its aglycone (22f) compared with initial leads 1 and 2. Moreover, the superior efficacy of 14c in various carbohydrate tolerance tests in diabetic rat models was confirmed compared with acarbose, an α-glucosidase inhibitor (α-GI) widely used in the clinic.

The proximal C-terminus of alpha(1C) subunits is necessary for junctional membrane targeting of cardiac L-type calcium channels

In cardiac myocytes, LTCCs (L-type calcium channels) form a functional signalling complex with ryanodine receptors at the JM (junctional membrane). Although the specific localization of LTCCs to the JM is critical for excitation-contraction coupling, their targeting mechanism is unclear. Transient transfection of GFP (green fluorescent protein)-α(1S) or GFP-α(1C), but not P/Q-type calcium channel α(1A), in dysgenic (α(1S)-null) GLT myotubes results in correct targeting of these LTCCs to the JMs and restoration of action-potential-induced Ca2+ transients. To identify the sequences of α(1C) responsible for JM targeting, we generated a range of α(1C)-α(1A) chimaeras, deletion mutants and alanine substitution mutants and studied their targeting properties in GLT myotubes. The results revealed that amino acids L(1681)QAGLRTL(1688) and P(1693)EIRRAIS(1700), predicted to form two adjacent α-helices in the proximal C-terminus, are necessary for the JM targeting of α(1C). The efficiency of restoration of action-potential-induced Ca2+ transients in GLT myotubes was significantly decreased by mutations in the targeting motif. JM targeting was not disrupted by the distal C-terminus of α(1C) which binds to the second α-helix. Therefore we have identified a new structural motif in the C-terminus of α(1C) that mediates the targeting of cardiac LTCCs to JMs independently of the interaction between proximal and distal C-termini of α(1C).